An electrical connection box used to connect wiring harnesses of an automotive vehicle is, as shown in FIG. 3, provided with upper casing 1 and lower casing 2. Layered element 10, including busbars 3 to 6 for forming an internal circuit, and insulating plates 7 to 9, is accommodated in a space defined by casings 1 and 2. Busbars 3 to 6 are connected via connectors 13 to relays 11 and fuses 12 mounted in receptacles formed on the upper surface of upper casing 1.
As shown in detail in FIG. 4, in layered element 10, first tier busbars 3 are arranged on the upper surface of upper insulating plate 7, second tier busbars 4 are located on the upper surface of intermediate insulating plate 8, third tier busbars 5 are on the upper surface of lower insulating plate 9, and fourth tier busbars 6 are on the lower surface of lower insulating plate 9.
The lower surface of upper insulating plate 7 and the lower surface of intermediate insulating plate 8 are in contact with the upper surfaces of ribs 8a in intermediate insulating plate 8 and the upper surfaces of ribs 9a in the lower insulating plate 9, respectively. Further, the lower surface of upper insulating plate 7 and the lower surface of intermediate plate 8 are substantially in contact with the upper surfaces of second tier busbars 4 and the upper surfaces of third tier busbars 5, respectively.
However, the layered element 10 requires three insulating plates 7 to 9 to arrange four layers of busbars 3 to 6. This leads to an increased number of parts, increased weight of the electrical connection box, and consequently to increased production cost for layered element 10.